おたんこなす

noun

fool; idiot; bird-brain

A mildly insulting, somewhat old-fashioned or playful term for a foolish person. Not extremely vulgar, but clearly derogatory.

• あんなおたんこなすに騙だまされるなんて、我われながら情なさけない。

  I can't believe I was tricked by such a fool; I'm ashamed of myself.

• おたんこなす！何なにやってんだよ。

  You idiot! What are you doing?